In the manufacture of paper products in either a single or twin fabric forming section of a papermaking machine, a highly fluid stock is delivered as a precisely controlled jet from a headbox 1 through a slice opening 2 onto a moving forming fabric as it passes around a breast roll and over a forming board or shoe (see FIG. 1). The headbox 1 and slice 2 are key parts of the papermaking process as together they will determine, to a great extent, the uniformity and formation properties of the finished sheet.
FIG. 2 illustrates the known arrangement in more detail. The headbox slice 2 controls the volume of stock and the angle of impingement of the stock jet 8 delivered onto the forming fabric 9 which is supported by the breast roll 11. It is important to maintain the headbox slice 2 opening at a constant cross-sectional area so as to produce a uniform paper web. The angle of impingement is controlled by the position of the slice lip 3 of the headbox slice 2 in relation to the apron 5, or bottom lip; this position is referred to as the setback L. As the slice lip 3 can be moved both up and down as well rotationally, its movement either upstream or downstream relative to the apron 5 will change the point of impingement resulting in a noticeable impact on sheet formation. The angle of impingement of the stock jet, and thus the position of the point of impingement on the forming fabric, is determined by the ratio L/b, where L is the setback, or relative location of the slice lip 3 with respect to the edge or tip 6 of the apron 5, and b is the height of the slice lip opening above the apron 5 (see FIG. 2).
The position of the tip 4 of the slice lip 3 relative to the position of the tip 6 of the lower apron 5 is critical for locating the point of impingement of the stock jet and to regulate the volume of stock flow from the headbox. When the ratio L/b≈0.5, then the angle of impingement of the stock jet is relatively steep, creating a situation referred to as “pressure forming”; when the ratio L/b≧1, then the angle of impingement is comparatively flatter and the jet travels relatively parallel to the fabric for a longer distance, creating a configuration referred to as “velocity forming”. Each configuration creates differing effects on the formation of the web, and both are commonly used for various purposes. Accurate measurement and control of both the slice lip opening b and setback L are thus extremely important with respect to the properties and quality of the paper product produced by the papermaking machine. Papermakers and service technicians must periodically verify both of these factors to ensure that neither has drifted from the “home position” over time, as well as make adjustments to the position of the slice lip 3 if it has moved. However, because of the proximity of the slice to the breast roll, it is often difficult to directly measure both of these critical parameters.
In the past, tapered blocks and/or “sliding parallels” have been used to measure the opening b but consistent measurement of the slice lip setback L required opening the headbox doors and/or lowering the breast roll to obtain access, and using a separate tool. It will be appreciated that either or both of these tasks is laborious and time consuming. What is needed then is a simple tool which will allow for simultaneous and accurate measurement of both the slice opening b and the setback L without necessitating either opening the headbox or moving the breast roll. The present invention provides a device which provides for such measurement without requiring specialized access or movement of any components adjacent the headbox.